Folk medicine (also known as traditional medicine) was medicine or treatment based on traditional knowledge rather than scientific practice.
In 2370, Quark brought a "medicinal brew" to Julian Bashir that was supposed to impart great energy and vigor but admitted that as a man of science, Bashir probably didn't believe in folk medicine. Bashir responded that one would be surprised just how often traditional medicine turned out to have genuine value. (DS9: "Rivals")